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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 7 — Mar. 26, 2012
  • pp: 6989–7001
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The development and application of femtosecond laser systems

W. Sibbett, A. A. Lagatsky, and C. T. A. Brown  »View Author Affiliations


Optics Express, Vol. 20, Issue 7, pp. 6989-7001 (2012)
http://dx.doi.org/10.1364/OE.20.006989


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Abstract

Some background as well as recent progress in the development of femtosecond lasers are discussed together with a brief outline of a few representative emergent applications in biology and medicine that are underpinned by access to such sources. We also provide a short summary of other contributions in this focus issue.

© 2012 OSA

1. Introduction

1.1 Historical background

The development of a diverse range of laser sources operating in the femtosecond time domain, and more recently in the sub-femtosecond region, has been a consistent theme within the photonics research sector for much of the past two decades. Although the publication of the first results of the self-mode-locked Ti:sapphire laser is acknowledged as being a key transition point [2

2. D. E. Spence, P. N. Kean, and W. Sibbett, “60-fsec pulse generation from a self-mode-locked Ti:sapphire laser,” Opt. Lett. 16(1), 42–44 (1991). [CrossRef] [PubMed]

], it is well known that the field of ultrafast optics emerged from pioneering mode locking studies of solid-state and organic dye lasers in the 1960s and early 1970s [3

3. A. J. DeMaria, D. A. Stetser, and H. Heynau, “Self Mode-Locking of Lasers with Saturable Absorbers,” Appl. Phys. Lett. 8(7), 174–176 (1966). [CrossRef]

,4

4. C. V. Shank and E. P. Ippen, “Subpicosecond kilowatt pulses from a mode-locked cw dye laser,” Appl. Phys. Lett. 24(8), 373–375 (1974). [CrossRef]

]. Whilst practical investigations were on-going, seminal contributions to the underpinning theory were produced by Haus [5

5. H. A. Haus, “Theory of Mode-Locking with a Fast Saturable Absorber,” J. Appl. Phys. 46(7), 3049–3058 (1975). [CrossRef]

,6

6. H. A. Haus, “Theory of Mode-Locking with a Slow Saturable Absorber,” IEEE J. Quantum Electron. 11(9), 736–746 (1975). [CrossRef]

] and New [7

7. G. H. C. New, “The Generation of Ultrashort Laser-Pulses,” Rep. Prog. Phys. 46(8), 877–971 (1983). [CrossRef]

]. Although organic dye solutions provided adequate gain bandwidths in colliding-pulse, passively mode-locked dye lasers to facilitate the generation of sub-100fs optical pulses [8

8. R. L. Fork, B. I. Greene, and C. V. Shank, “Generation of Optical Pulses Shorter than 0.1 psec by Colliding Pulse Mode-Locking,” Appl. Phys. Lett. 38(9), 671–672 (1981). [CrossRef]

], the poor practicality and low efficiency features of such lasers consigned them mainly to laboratory setups.

Despite their limitations, there were many impressive research-based applications using femtosecond dye lasers in either oscillator [9

9. A. M. Weiner and E. P. Ippen, “Novel transient scattering technique for femtosecond dephasing measurements,” Opt. Lett. 9(2), 53–55 (1984). [CrossRef] [PubMed]

] or oscillator-amplifier configurations [9

9. A. M. Weiner and E. P. Ippen, “Novel transient scattering technique for femtosecond dephasing measurements,” Opt. Lett. 9(2), 53–55 (1984). [CrossRef] [PubMed]

]. From the historical perspective, it should also be recognized that in the 1980s, whenever some research emphasis transferred to the study of nonlinear effects in optical fibers, a significant international effort was devoted to femtosecond lasers that operated in the near-infrared spectral region where color-center crystals were used as the gain media [10

10. L. F. Mollenauer and R. H. Stolen, “The soliton laser,” Opt. Lett. 9(1), 13–15 (1984). [CrossRef] [PubMed]

]. Although sharing the common drawback of a lack of day-to-day practicality, it is important to appreciate how the knowledge base from these early types of femtosecond lasers subsequently shaped the development of the post-1990 categories of the much more practical and versatile ultrashort-pulse sources that ushered in an era where access to, for example, attosecond-duration pulses [11

11. P. B. Corkum, N. H. Burnett, and M. Y. Ivanov, “Subfemtosecond pulses,” Opt. Lett. 19(22), 1870–1872 (1994). [CrossRef] [PubMed]

] and stabilized frequency combs [12

12. S. A. Diddams, “The evolving optical frequency comb,” J. Opt. Soc. Am. B 27(11), B51–B62 (2010). [CrossRef]

] has become relatively straight forward.

Although the simplicity, versatility and high-power performance characteristics of the KLM Ti:sapphire lasers were to be welcomed, the requirement to optimize cavity-design parameters to facilitate the exploitation of the optical Kerr effect [16

16. G. Cerullo, S. De Silvestri, V. Magni, and L. Pallaro, “Resonators for Kerr-lens mode-locked femtosecond Ti:sapphire lasers,” Opt. Lett. 19(11), 807–809 (1994). [CrossRef] [PubMed]

] represented an operational challenge to the implementation of the KLM technique more generally. Fortunately, this design constraint was alleviated substantially by the availability of semiconductor saturable absorber mirrors (SESAMs) [17

17. U. Keller, K. J. Weingarten, F. X. Kärtner, D. Kopf, B. Braun, I. D. Jung, R. Fluck, C. Honninger, N. Matuschek, and J. A. derAu, “Semiconductor saturable absorber mirrors (SESAM's) for femtosecond to nanosecond pulse generation in solid-state lasers,” IEEE J. Sel. Top. Quantum Electron. 2(3), 435–453 (1996). [CrossRef]

] and saturable Bragg reflectors (SBRs) [18

18. S. Tsuda, W. H. Knox, S. T. Cundiff, W. Y. Jan, and J. E. Cunningham, “Mode-locking ultrafast solid-state lasers with saturable Bragg reflectors,” IEEE J. Sel. Top. Quantum Electron. 2(3), 454–464 (1996). [CrossRef]

] that could be incorporated to initiate and sustain the relevant self-mode-locking processes. With careful design consideration of broadband semiconductor saturable absorber mirrors used in conjunction with double-chirped resonator mirrors, it has been shown that it is possible to accompany a self-starting KLM laser operation with access to a large proportion of the gain bandwidth to produce pulses as short as 6.5 fs [19

19. D. H. Sutter, I. D. Jung, F. X. Kärtner, N. Matuschek, F. Morier-Genoud, V. Scheuer, M. Tilsch, T. Tschudi, and U. Keller, “Self-starting 6.5-fs pulses from a Ti:sapphire laser using a semiconductor saturable absorber and double-chirped mirrors,” IEEE J. Sel. Top. Quantum Electron. 4(2), 169–178 (1998). [CrossRef]

]. Over the past two decades, continuing substantial effort has been devoted to the design and development of a wide range of SESAM/SBR options [20

20. U. Keller, ““Ultrafast solid-state laser oscillators: a success story for the last 20 years with no end in sight,”,” Appl. Phys. B 100(1), 15–28 (2010). [CrossRef]

] so that, when required, there can be an availability of such devices that have compatibility with most femtosecond laser types and including a growing range of solid-state, semiconductor and fiber lasers. Indeed, developments in this area have underpinned a range of commercial femtosecond laser systems that require the reliable “turn key” pulsed operation enabled by SESAM devices.

2. Source developments

Rather than deal with every aspect of source development that has occurred in the past two decades, it suffices within the context of this paper to highlight a few specific advances that have served to enlarge the applications space for coherent femtosecond optical pulses. This selection is made feasible by identifying some of the new gain media and control techniques that have impacted the operational status and the enhanced versatility of modern femtosecond-laser configurations.

The diversity of ultrashort pulse laser oscillators is illustrated in Fig. 1
Fig. 1 A plot of peak power versus average power for a range of ultrashort pulse laser oscillator technologies. Also included are indicative application areas placed in appropriate regions of laser performance. The inset in the figure shows the performance of the sources indicated.
that shows a plot of peak power versus average power. Indicative positions are given for the key source technologies, though it must be acknowledged that the performance from each type of source may vary outside these limits particularly when extra-cavity amplification / pulse compression is undertaken. Also placed in the figure are three applications sectors with desirable source parameters. It is interesting to note that oscillators continue to develop rapidly enabling broad coverage of the peak power / average power space to be achieved and opening up new fields of application.

2.1 Solid-state lasers

Interestingly, while the basic setup for the archetypal KLM Ti:sapphire laser remains a foundation on which many subsequent system developments have been based, a common and desirable feature is that the gain media should lend themselves to diode laser pumping and facilitate access to smooth and broad lasing spectra. In this regard, further progress in the identification of novel gain media resulted in the development of a range of ultrafast solid-state lasers that are compatible with direct laser diode pumping and that operate from the near/mid-infrared spectral range. In particular, Cr3+-doped colquiriites (Cr:LiSAF, Cr:LiCAF, and Cr:LiSGaF) (0.8-0.9 µm) represent currently low-cost alternatives to Ti:sapphire laser technology [21

21. U. Demirbas, D. Li, J. R. Birge, A. Sennaroglu, G. S. Petrich, L. A. Kolodziejski, F. X. Kaertner, and J. G. Fujimoto, “Low-cost, single-mode diode-pumped Cr:Colquiriite lasers,” Opt. Express 17(16), 14374–14388 (2009). [CrossRef] [PubMed]

]. Cr4+-doped Mg2SiO4 (forsterite) [22

22. C. Chudoba, J. G. Fujimoto, E. P. Ippen, H. A. Haus, U. Morgner, F. X. Kärtner, V. Scheuer, G. Angelow, and T. Tschudi, “All-solid-state Cr:forsterite laser generating 14-fs pulses at 1.3 mum,” Opt. Lett. 26(5), 292–294 (2001). [CrossRef] [PubMed]

] and Y3Al5O12 (YAG) [23

23. D. J. Ripin, C. Chudoba, J. T. Gopinath, J. G. Fujimoto, E. P. Ippen, U. Morgner, F. X. Kärtner, V. Scheuer, G. Angelow, and T. Tschudi, “Generation of 20-fs pulses by a prismless Cr(4+):YAG laser,” Opt. Lett. 27(1), 61–63 (2002). [CrossRef] [PubMed]

] laser systems are able to support the generation of high-energy sub-50 fs pulses in the 1.3 μm and 1.55 μm regions which are ideal for many biological [24

24. B. E. Bouma, G. J. Tearney, I. P. Bilinsky, B. Golubovic, and J. G. Fujimoto, “Self-phase-modulated Kerr-lens mode-locked Cr:forsterite laser source for optical coherence tomography,” Opt. Lett. 21(22), 1839–1841 (1996). [CrossRef] [PubMed]

] and datacomms applications [25

25. Y. J. Chai, C. G. Leburn, A. A. Lagatsky, C. T. A. Brown, R. V. Penty, I. H. White, and W. Sibbett, “1.36-Tb/s spectral slicing source based on a Cr4+-YAG femtosecond laser,” J. Lightwave Technol. 23(3), 1319–1324 (2005). [CrossRef]

]. Cr2+-doped chalcogenide materials (Cr:ZnSe, Cr:ZnS) are an attractive option for broadband femtosecond laser developments in the mid-IR (~2.4 μm) [26

26. E. Sorokin, S. Naumov, and I. T. Sorokina, “Ultrabroadband infrared solid-state lasers,” IEEE J. Sel. Top. Quantum Electron. 11(3), 690–712 (2005). [CrossRef]

] which are especially well suited to sensitive and high-resolution molecular spectroscopy [27

27. S. A. Diddams, L. Hollberg, and V. Mbele, “Molecular fingerprinting with the resolved modes of a femtosecond laser frequency comb,” Nature 445(7128), 627–630 (2007). [CrossRef] [PubMed]

,28

28. E. Sorokin, I. T. Sorokina, J. Mandon, G. Guelachvili, and N. Picque, “Sensitive multiplex spectroscopy in the molecular fingerprint 2.4 mum region with a Cr(2+):ZnSe femtosecond laser,” Opt. Express 15(25), 16540–16545 (2007). [CrossRef] [PubMed]

].

Although crystalline gain media with rare-earth ion doping (Nd3+, Yb3+, Er3+, Tm3+, Ho3+) do not offer such broadband gain spectra as their transition-metal counterparts, the distinctively attractive features of this class of laser include low operational threshold, high efficiency and an ability to be configured into extremely compact configurations. Indeed, pulse repetition frequencies up to 160 GHz and 100 GHz for picosecond-pulse generation have been demonstrated for Nd:YVO4 [29

29. L. Krainer, R. Paschotta, S. Lecomte, M. Moser, K. J. Weingarten, and U. Keller, “Compact Nd: YVO4 lasers with pulse repetition rates up to 160 GHz,” IEEE J. Quantum Electron. 38(10), 1331–1338 (2002). [CrossRef]

] and Er:glass [30

30. A. E. H. Oehler, T. Südmeyer, K. J. Weingarten, and U. Keller, “100 GHz passively mode-locked Er:Yb:glass laser at 1.5 microm with 1.6-ps pulses,” Opt. Express 16(26), 21930–21935 (2008). [CrossRef] [PubMed]

] mode-locked oscillators operating around 1 μm and 1.5 μm, respectively. More recently, low-cost, efficient and compact femtosecond laser systems become widely available around 1 μm due to the introduction a range of Yb3+-doped gain media assisted by the timely and rapid progress in the production of InGaAs-based pump laser diodes. Currently, ytterbium-based femtosecond lasers produce pulses as short as 35 fs (Yb:YCOB) [31

31. A. Yoshida, A. Schmidt, V. Petrov, C. Fiebig, G. Erbert, J. H. Liu, H. J. Zhang, J. Y. Wang, and U. Griebner, “Diode-pumped mode-locked Yb:YCOB laser generating 35 fs pulses,” Opt. Lett. 36(22), 4425–4427 (2011). [CrossRef] [PubMed]

] and operate with an optical-to-optical efficiency that can reach 50% [32

32. A. A. Lagatsky, C. T. A. Brown, and W. Sibbett, “Highly efficient and low threshold diode-pumped Kerr-lens mode-locked Yb:KYW laser,” Opt. Express 12(17), 3928–3933 (2004). [CrossRef] [PubMed]

]. When deployed in a thin-disk laser configuration that offers efficient heat removal capabilities [33

33. A. Giesen, H. Hugel, A. Voss, K. Wittig, U. Brauch, and H. Opower, ““Scalable Concept for Diode-Pumped High-Power Solid-State Lasers,” Appl. Phys. B 58(5), 365–372 (1994). [CrossRef]

], Yb-based lasers can generate average powers up to 141 W at a pulse duration of 738 fs (Yb:Lu2O3) [34

34. C. R. E. Baer, C. Kränkel, C. J. Saraceno, O. H. Heckl, M. Golling, R. Peters, K. Petermann, T. Südmeyer, G. Huber, and U. Keller, “Femtosecond thin-disk laser with 141 W of average power,” Opt. Lett. 35(13), 2302–2304 (2010). [CrossRef] [PubMed]

]. It should be noted that higher average powers are only available currently from more complex oscillator-amplifier systems such as a fiber laser with a chirped-pulse-amplifier (830 W, 640 fs) [35

35. T. Eidam, S. Hanf, E. Seise, T. V. Andersen, T. Gabler, C. Wirth, T. Schreiber, J. Limpert, and A. Tünnermann, “Femtosecond fiber CPA system emitting 830 W average output power,” Opt. Lett. 35(2), 94–96 (2010). [CrossRef] [PubMed]

] or using a slab amplifier (400 W, 680 fs) [36

36. P. Russbueldt, T. Mans, G. Rotarius, J. Weitenberg, H. D. Hoffmann, and R. Poprawe, “400W Yb:YAG Innoslab fs-Amplifier,” Opt. Express 17(15), 12230–12245 (2009). [CrossRef] [PubMed]

]. It can therefore be expected that Yb-laser systems that produce sufficient peak powers directly to enable efficient nonlinear frequency conversion in processes such as high harmonic generation or octave-spanning supercontinuum generation in a photonic crystal fiber [37

37. S. Pekarek, T. Südmeyer, S. Lecomte, S. Kundermann, J. M. Dudley, and U. Keller, “Self-referenceable frequency comb from a gigahertz diode-pumped solid-state laser,” Opt. Express 19(17), 16491–16497 (2011). [CrossRef] [PubMed]

] will facilitate the additional demands of an ever-growing applications sector. This will be especially true where physical compactness, low cost and robustness represent the desired attributes.

This developmental progress is ongoing in ultrafast solid-state lasers where, for example, quantum-dot-based SESAMs [38

38. A. A. Lagatsky, C. G. Leburn, C. T. A. Brown, W. Sibbett, S. A. Zolotovskaya, and E. U. Rafailov, “Ultrashort-pulse lasers passively mode locked by quantum-dot-based saturable absorbers,” Prog. Quantum Electron. 34(1), 1–45 (2010). [CrossRef]

] that are characterized by faster response times and lower saturation fluencies than their quantum-well counterparts can facilitate efficient mode locking at high repetition rates. Another direction in ultrafast laser technology has been facilitated by the introduction of carbon nanotubes [39

39. T. R. Schibli, K. Minoshima, H. Kataura, E. Itoga, N. Minami, S. Kazaoui, K. Miyashita, M. Tokumoto, and Y. Sakakibara, “Ultrashort pulse-generation by saturable absorber mirrors based on polymer-embedded carbon nanotubes,” Opt. Express 13(20), 8025–8031 (2005). [CrossRef] [PubMed]

] and graphene [40

40. Z. P. Sun, T. Hasan, F. Torrisi, D. Popa, G. Privitera, F. Q. Wang, F. Bonaccorso, D. M. Basko, and A. C. Ferrari, “Graphene mode-locked ultrafast laser,” ACS Nano 4(2), 803–810 (2010). [CrossRef] [PubMed]

] as saturable absorbers. These offer the key advantages of ultrabroad operating range from the near- to-mid infrared (especially in case of grapheme [41

41. K. F. Mak, M. Y. Sfeir, Y. Wu, C. H. Lui, J. A. Misewich, and T. F. Heinz, “Measurement of the optical conductivity of graphene,” Phys. Rev. Lett. 101(19), 196405 (2008). [CrossRef] [PubMed]

]), ultrafast recovery time [42

42. R. W. Newson, J. Dean, B. Schmidt, and H. M. van Driel, “Ultrafast carrier kinetics in exfoliated graphene and thin graphite films,” Opt. Express 17(4), 2326–2333 (2009). [CrossRef] [PubMed]

] with fabrication techniques that do not require the use of costly clean room facilities. Moreover, such nonlinear media can be deposited onto any intracavity element thereby making the design of solid-state lasers ever more practical and physically compact.

2.2 Fiber lasers

The outstanding research undertaken on fiber lasers and fiber amplifiers in the 1980s provided a robust scientific and technological base for the subsequent development of a wide range of fiber-based ultrafast sources that continue to find increased applicability together with attractive user compatibility. Whilst in their earliest embodiments femtosecond fiber lasers often struggled to attain the levels of pulse energy and peak power associated with solid-state mode-locked lasers, more recently developed options have revealed the operational potential of these systems. For instance, in 2005 Buckley et al demonstrated a fiber laser that produced sub-100 fs pulses having a pulse energy of 14nJ and peak power at the 100 kW level [43

43. J. R. Buckley, F. W. Wise, F. O. Ilday, and T. Sosnowski, “Femtosecond fiber lasers with pulse energies above 10 nJ,” Opt. Lett. 30(14), 1888–1890 (2005). [CrossRef] [PubMed]

]. More complex, but still compact, source arrangements have also yielded exceptionally short pulse durations of 8 fs [44

44. A. Sell, G. Krauss, R. Scheu, R. Huber, and A. Leitenstorfer, “8-fs pulses from a compact Er:fiber system: quantitative modeling and experimental implementation,” Opt. Express 17(2), 1070–1077 (2009). [CrossRef] [PubMed]

], high repetition frequencies (10 GHz) [45

45. G. Sobon, K. Krzempek, P. Kaczmarek, K. M. Abramski, and M. Nikodem, “10 GHz passive harmonic mode-locking in Er-Yb double-clad fiber laser,” Opt. Commun. 284(18), 4203–4206 (2011). [CrossRef]

] and through the possibility to engineer the fiber gain medium, MW level peak power (>10 W average power) devices [46

46. S. Lefrançois, K. Kieu, Y. J. Deng, J. D. Kafka, and F. W. Wise, “Scaling of dissipative soliton fiber lasers to megawatt peak powers by use of large-area photonic crystal fiber,” Opt. Lett. 35(10), 1569–1571 (2010). [CrossRef] [PubMed]

]. A further interesting feature of fiber-based systems is their potential to deliver new mode locking schemes such as the recently demonstrated soliton-similariton technique through careful dispersion management [47

47. B. Oktem, C. Ülgüdür, and F. Ö. Ilday, “Soliton-similariton fibre laser,” Nat. Photonics 4(5), 307–311 (2010). [CrossRef]

]. Femtosecond fiber lasers have now matured into an applicable technology that is being deployed, for example, in metrology [48

48. G. Marra, R. Slavík, H. S. Margolis, S. N. Lea, P. Petropoulos, D. J. Richardson, and P. Gill, “High-resolution microwave frequency transfer over an 86-km-long optical fiber network using a mode-locked laser,” Opt. Lett. 36(4), 511–513 (2011). [CrossRef] [PubMed]

], bio-science [49

49. J. R. Unruh, E. S. Price, R. G. Molla, L. Stehno-Bittel, C. K. Johnson, and R. Q. Hui, “Two-photon microscopy with wavelength switchable fiber laser excitation,” Opt. Express 14(21), 9825–9831 (2006). [CrossRef] [PubMed]

] and materials processing [50

50. R. R. Thomson, N. D. Psaila, S. J. Beecher, and A. K. Kar, “Ultrafast laser inscription of a high-gain Er-doped bismuthate glass waveguide amplifier,” Opt. Express 18(12), 13212–13219 (2010). [CrossRef] [PubMed]

].

Generally, femtosecond fiber lasers are based on transitions from rare-earth ions operating in the near-infrared and are often based on Yb-, Er- or Tm-doped gain media. Their relatively high peak powers are well matched to nonlinear optical conversion and indeed a range of commercial products are now available which give comparable performance to Ti:sapphire oscillators (e.g. IMRA Femtolite FX-100 or PolarOnyx Mercury Lasers.) The output from fiber lasers is also well matched to the photonic crystal fibers that are often used to generate supercontinuum radiation from which a range of all-fiber-supercontinuum sources have been developed [51

51. N. Nishizawa and J. Takayanagi, “Octave spanning high-quality supercontinuum generation in all-fiber system,” J. Opt. Soc. Am. B 24(8), 1786–1792 (2007). [CrossRef]

]. This versatility of performance when combined with their inherent practicality makes modern femtosecond fiber lasers a very important enlargement of the ultrafast source portfolio that is available to scientists and technologists for applications that now span a broad range of disciplines.

2.3 Semiconductor lasers

Although it would seem attractive to have stand-alone, electrically-pumped, semiconductor diode lasers as user-compatible sources of femtosecond optical pulses having comparable characteristics to those produced by solid-state or fiber lasers, but progress to date toward this objective has been rather limited. While gain media based on quantum-dot semiconductor structures do offer some access to enlarged bandwidths and the generation of sub-picosecond optical pulses at 20GHz repetition rates has been reported [52

52. E. U. Rafailov, M. A. Cataluna, W. Sibbett, N. D. Il'inskaya, Y. M. Zadiranov, A. E. Zhukov, V. M. Ustinov, D. A. Livshits, A. R. Kovsh, and N. N. Ledentsov, “High-power picosecond and femtosecond pulse generation from a two-section mode-locked quantum-dot laser,” Appl. Phy. Lett. 87(2005).

] there are still questions as to the generation of truly femtosecond-duration coherent pulses from a laser of this type. An interesting class of devices based on super-radiant emission from quantum-dot structures has also been recently reported [53

53. P. P. Vasil'ev, “Femtosecond superradiant emission in inorganic semiconductors,” Rep. Prog. Phys. 72(7), 076501 (2009). [CrossRef]

]. Whilst research in this area remains ongoing such technologies hold out the potential for femtosecond semiconductor devices with pulse repetition frequencies in the low MHz region and thus the high peak powers more often associated with solid-state laser systems [54

54. M. Xia, R. V. Penty, I. H. White, and P. P. Vasil'ev, “Superradiant Emission from a Tapered Quantum-Dot Semiconductor Diode Emitter,” 2010 Conference on Lasers and Electro-Optics (CLEO) and Quantum Electronics and Laser Science Conference (QELS) (2010).

].

The alternative schemes involving optical pumping with extended external cavities with vertical-cavity, surface-emitting semiconductor gain chips [VECSELs] [55

55. U. Keller and A. C. Tropper, ““Passively modelocked surface-emitting semiconductor lasers,” Phys. Rep.-Rev. Sec. Phys. Lett. 429, 67–120 (2006).

] represent a much more feasible approach for the device options that are available at present. Using this arrangement pulse durations as short as 60 fs have been achieved [56

56. A. H. Quarterman, K. G. Wilcox, V. Apostolopoulos, Z. Mihoubi, S. P. Elsmere, I. Farrer, D. A. Ritchie, and A. Tropper, “A passively mode-locked external-cavity semiconductor laser emitting 60-fs pulses,” Nat. Photonics 3(12), 729–731 (2009). [CrossRef]

] and recent experimental demonstrations have yielded pulse durations in the 800fs regime at average power levels exceeding 1W and around 400 fs at an average power just below 150 mW have been reported for a VECSEL operated at a central wavelength of 970nm [57

57. M. Hoffmann, O. D. Sieber, V. J. Wittwer, I. L. Krestnikov, D. A. Livshits, Y. Barbarin, T. Südmeyer, and U. Keller, “Femtosecond high-power quantum dot vertical external cavity surface emitting laser,” Opt. Express 19(9), 8108–8116 (2011). [CrossRef] [PubMed]

] and peak powers in excess of 300 W from a GHz PRF device [58

58. K. G. Wilcox, A. H. Quarterman, H. Beere, D. A. Ritchie, and A. C. Tropper, “High Peak Power Femtosecond Pulse Passively Mode-Locked Vertical-External-Cavity Surface-Emitting Laser,” IEEE Photon. Technol. Lett. 22(14), 1021–1023 (2010). [CrossRef]

]. It is noteworthy that in this instance both the saturable absorber and gain elements were quantum-dot-based and the achievement of an average power in the 1W regime is a very encouraging result for an attractively compact design of femtosecond laser.

2.4 The control of femtosecond lasers

One clear objective in the refinement of femtosecond laser designs is to produce sources that are versatile and adaptable to permit the user to choose the specific operating condition which best suits a specific application. In many cases there have been great advances in the extra-cavity control of the output from ultrafast lasers allowing, for example, pulses with specifically controlled wavelength / profiles to be produced through the use of liquid crystal phase modulators [59

59. A. M. Weiner, D. E. Leaird, J. S. Patel, and J. R. Wullert, “Programmable Shaping of Femtosecond Optical Pulses by Use of 128-Element Liquid-Crystal Phase Modulator,” IEEE J. Quantum Electron. 28(4), 908–920 (1992). [CrossRef]

] or deformable mirrors [60

60. J. Garduño-Mejía, A. H. Greenaway, and D. T. Reid, “Designer femtosecond pulses using adaptive optics,” Opt. Express 11(17), 2030–2040 (2003). [CrossRef] [PubMed]

]. Whilst such approaches offer excellent performance, perhaps the simplest approach to control is to influence the intracavity behavior of the laser thereby permitting the direct control of the oscillator output. Recent demonstrations with the authors’ laboratory has shown that intracavity deformable mirrors may also be used to control several aspects of laser behavior including phase profiles and pulse durations [61

61. N. K. Metzger, W. Lubeigt, D. Burns, M. Griffith, L. Laycock, A. A. Lagatsky, C. T. A. Brown, and W. Sibbett, “Ultrashort-pulse laser with an intracavity phase shaping element,” Opt. Express 18(8), 8123–8134 (2010). [CrossRef] [PubMed]

].

A further goal relates to direct control of the laser through the manipulation of other components within the laser cavity. One component that has the clear potential to provide some element of control is the SESAM/SBR that is often used to initiate and sustain mode locking. In these devices, the quantum-confined structures can be externally manipulated through both optical and electronic means to provide some level of active control over a passive structure. One example is the use of an external laser diode beam to provide direct and rapid (~75 μs) heating of an SBR coincident with the intracavity laser spot to provide controllable switching between CW and mode-locked operation [62

62. V. G. Savitski, A. J. Kemp, S. Calvez, and D. Burns, “Optically Pumped Saturable Bragg Reflectors: Nonlinear Spectroscopy and Application in Ultrafast Lasers,” IEEE J. Quantum Electron. 46(11), 1650–1655 (2010). [CrossRef]

]. Electronic control of saturable mirrors in solid-state lasers has also been demonstrated and SESAMs which offer controllable modulation depths [63

63. X. M. Liu, E. U. Rafailov, D. Livshits, and D. Turchinovich, “Quantum well saturable absorber mirror with electrical control of modulation depth,” Appl. Phys. Lett. 97(5), 051103 (2010). [CrossRef]

] and tunable pulse durations from 17.4 ps to 6.4 ps [64

64. S. A. Zolotovskaya, K. G. Wilcox, A. Abdolvand, D. A. Livshits, and E. U. Rafailov, “Electronically Controlled Pulse Duration Passively Mode-Locked Cr:Forsterite Laser,” IEEE Photon. Technol. Lett. 21(16), 1124–1126 (2009). [CrossRef]

] and these serve to illustrate the promise of this approach for producing easily controlled output from ultrafast lasers.

Control of the pulse repetition frequency (PRF) of femtosecond lasers remains a challenge as the PRF is generally set by the round-trip time of a single pulse circulating within the cavity. Some progress has been made in this area by the use of subsidiary Fabry-Perot (F-P) cavities that are length matched to harmonics of the primary cavity to provide PRF multiplication. In this regard, Chen et al have used a dispersion-compensated F-P cavity to multiply the repetition frequency of a femtosecond Er-fiber laser from 200 MHz to 2 GHz [65

65. J. Chen, J. W. Sickler, P. Fendel, E. P. Ippen, F. X. Kärtner, T. Wilken, R. Holzwarth, and T. W. Hänsch, “Generation of low-timing-jitter femtosecond pulse trains with 2 GHz repetition rate via external repetition rate multiplication,” Opt. Lett. 33(9), 959–961 (2008). [CrossRef] [PubMed]

]. A complementary approach that has been used to obtain PRF-tuning in the kHz to MHz regime is through cavity dumping that can be used to obtain MW peak powers directly from laser oscillators. Killi et al have shown that a diode-pumped Yb:glass laser can produce 1.5 MW peak power pulses at a pulse repetition frequency of 500 kHz [66

66. A. Killi, J. Dörring, U. Morgner, M. J. Lederer, J. Frei, and D. Kopf, “High speed electro-optical cavity dumping of mode-locked laser oscillators,” Opt. Express 13(6), 1916–1922 (2005). [CrossRef] [PubMed]

].

3. Some representative applications in biology and medicine

3.1 Nonlinear spectroscopic and fluorescence techniques

A very well known and trailblazing use of ultrafast lasers relates to two-photon microscopy [72

72. W. Denk, J. H. Strickler, and W. W. Webb, “Two-photon laser scanning fluorescence microscopy,” Science 248(4951), 73–76 (1990). [CrossRef] [PubMed]

]. In this process, the focused near-infrared laser radiation is used to excite fluorescence from a region of interest. By contrast with a single-photon excitation at a shorter wavelength, in this case the excited region is defined by the three-dimensional positioning of the focal zone due to the intensity dependence of the nonlinear process, thereby allowing z-sectioning to be performed by adjusting the focal position without the need for a more complex confocal arrangement. By using excitation in the near-infrared where biological transmission is maximized, such techniques provide scope for in-depth tissue imaging and, when the average power is kept low, subject the sample to reduced heating compared to other approaches. Whilst in its early days this technique was confined within a laboratory, more recent developments in endoscopy are beginning to show clinical promise in deep tissue imaging [73

73. K. König, A. Ehlers, I. Riemann, S. Schenkl, R. Bückle, and M. Kaatz, “Clinical two-photon microendoscopy,” Microsc. Res. Tech. 70(5), 398–402 (2007). [CrossRef] [PubMed]

] and in in vivo brain imaging [74

74. R. P. J. Barretto, T. H. Ko, J. C. Jung, T. J. Wang, G. Capps, A. C. Waters, Y. Ziv, A. Attardo, L. Recht, and M. J. Schnitzer, “Time-lapse imaging of disease progression in deep brain areas using fluorescence microendoscopy,” Nat. Med. 17(2), 223–228 (2011). [CrossRef] [PubMed]

].

In recognizing that photonics-based techniques can offer complementarity with modalities such as MRI, research in stimulated Raman scattering (SRS) in particular, demonstrates clearly where femtosecond lasers can play a key role. Specifically, SRS microscopy has been developed to the point where video-rate imaging can begin to be an attractive asset in practical medical diagnostics. Indeed, building on the pioneering research being led by Xie’s group in Harvard University [75

75. X. S. Xie and J. X. Cheng, “Coherent anti-Stokes Raman scattering microscopy: Instrumentation, theory, and applications,” J. Phys. Chem. B 108(3), 827–840 (2004). [CrossRef]

] there have emerged several striking examples of highly specific and label-free molecular imaging where advantage is taken of an amplitude-shaping concept within SRS by using ‘spectrally-tailored excitation’ (or STE) in a scheme designated as STE-SRS [76

76. X. S. Xie, C. W. Freudiger, W. Min, G. R. Holtom, B. W. Xu, and M. Dantus, “Highly specific label-free molecular imaging with spectrally tailored excitation-stimulated Raman scattering (STE-SRS) microscopy,” Nat. Photonics 5(2), 103–109 (2011). [CrossRef]

]. This is made possible by combining broadband (femtosecond) and narrower band (picosecond) laser excitations to achieve STE-SRS microscopy with exceptional specificity and sensitivity in, for instance, the 3-D spectral imaging of protein [76

76. X. S. Xie, C. W. Freudiger, W. Min, G. R. Holtom, B. W. Xu, and M. Dantus, “Highly specific label-free molecular imaging with spectrally tailored excitation-stimulated Raman scattering (STE-SRS) microscopy,” Nat. Photonics 5(2), 103–109 (2011). [CrossRef]

].

3.2 Opthalmology

It is quite fascinating that lasers have retained a high profile throughout their history in various applications within ophthalmology. This is true also for the subset of femtosecond lasers for implementations ranging from corneal surgery [77

77. T. Juhasz, H. Frieder, R. M. Kurtz, C. Horvath, J. F. Bille, and G. Mourou, “Corneal refractive surgery with femtosecond lasers,” IEEE J. Sel. Top. Quantum Electron. 5(4), 902–910 (1999). [CrossRef]

] through to possibilities relating to photo-therapies for dealing with cataracts [78

78. N. Mamalis, “Femtosecond laser: the future of cataract surgery?” J. Cataract Refract. Surg. 37(7), 1177–1178 (2011). [CrossRef] [PubMed]

].

To be specific, the commercialized IntraLase procedure [79

79. P. S. Binder, “Flap dimensions created with the IntraLase FS laser,” J. Cataract Refract. Surg. 30(1), 26–32 (2004). [CrossRef] [PubMed]

] that evolved from initial fundamental and pioneering research undertaken at the University of Michigan [77

77. T. Juhasz, H. Frieder, R. M. Kurtz, C. Horvath, J. F. Bille, and G. Mourou, “Corneal refractive surgery with femtosecond lasers,” IEEE J. Sel. Top. Quantum Electron. 5(4), 902–910 (1999). [CrossRef]

] involves the use of femtosecond laser pulses that are focused to a point within the cornea with the creation of thousands of microscopic bubbles. The attraction of the IntraLase procedure is that an eye surgeon can design and control with high precision the physical aspects of a corneal flap such as its thickness, its circumference, and the angle of its edges, such that the protective flap can be tailored to an individual eye. The flap is then lifted to provide access to an excimer laser beam for photorefractive correction and the procedure is complete when the ‘hinged’ flap is securely repositioned on its beveled edge. This type of procedure lends itself to rapid healing and recovery and is well suited to patients having some corneal parameters (eg steep, flat or thin corneas) for whom surgery performed with a standard micro-keratome would be less appropriate. More recently, a procedure has been developed that relies entirely on a femtosecond laser system (femtosecond lenticular extraction – FLEx) based on a commercial instrument that removes the need for an excimer laser in the process [80

80. W. Sekundo, K. Kunert, C. Russmann, A. Gille, W. Bissmann, G. Stobrawa, M. Sticker, M. Bischoff, and M. Blum, “First efficacy and safety study of femtosecond lenticule extraction for the correction of myopia: six-month results,” J. Cataract Refract. Surg. 34(9), 1513–1520 (2008). [CrossRef] [PubMed]

].

The prospects for a non-invasive therapy involving femtosecond laser pulses in a two-photon-based procedure for the reversal of cataractous effects in the lens of the eye appear to be quite exciting. In this case, an induced photochemical bleaching of the accumulated yellow chromophores is being researched as a means of recovering at least some of the transparency within the lens of the eye [81

81. L. Kessel, L. Eskildsen, M. van der Poel, and M. Larsen, “Non-invasive bleaching of the human lens by femtosecond laser photolysis,” PLoS ONE 5(3), e9711 (2010). [CrossRef] [PubMed]

]. In these experiments to date involving human donor eyes, the raster-scanned, regeneratively-amplified femtosecond pulses from a Ti-sapphire laser (800 nm, 200-300 fs at 30-275 kHz pulse repetition frequency) have been shown to produce some degree of rejuvenation of the optical lens and so this approach if successful could have an enormous potential in healthcare as a cost effective means of addressing the compromised vision that arises from cataracts.

Interestingly, another two-photon process involving the photosensitization of singlet oxygen production can also be exploited within cardiac tissue engineering. In a recently reported study [82

82. K. Kuetemeyer, G. Kensah, M. Heidrich, H. Meyer, U. Martin, I. Gruh, and A. Heisterkamp, “Two-photon induced collagen cross-linking in bioartificial cardiac tissue,” Opt. Express 19(17), 15996–16007 (2011). [CrossRef] [PubMed]

], femtosecond pulses from a regeneratively-amplified Ti:sapphire laser were raster scanned over riboflavin-treated tissue to induce collagen cross linking and an increase in tissue stiffness was achieved without compromising cell viability in the region of exposure. This photonics-assisted route towards the generation of transplantable tissue surrogates having the necessary mechanical stability for cardiac surgery is therefore timely both as a potential therapy in its own right and as a means to address the recognized shortage of donor organs for transplantation [82

82. K. Kuetemeyer, G. Kensah, M. Heidrich, H. Meyer, U. Martin, I. Gruh, and A. Heisterkamp, “Two-photon induced collagen cross-linking in bioartificial cardiac tissue,” Opt. Express 19(17), 15996–16007 (2011). [CrossRef] [PubMed]

].

3.3. Femtosecond-enabled photoporation and transfection

On a cellular level rather than on the tissue scale just mentioned, femtosecond-laser-based photoporation that facilitates the optical transfection [83

83. U. K. Tirlapur and K. König, “Targeted transfection by femtosecond laser,” Nature 418(6895), 290–291 (2002). [CrossRef] [PubMed]

] or injection of other materials [84

84. C. McDougall, D. J. Stevenson, C. T. A. Brown, F. Gunn-Moore, and K. Dholakia, “Targeted optical injection of gold nanoparticles into single mammalian cells,” J Biophotonics 2(12), 736–743 (2009). [CrossRef] [PubMed]

] of biological cells is becoming a more widely used methodology in cell biology. This approach has the attraction that it offers cell specificity with high transfection efficiency as well as acceptable post-transfection cell viability [85

85. D. Stevenson, B. Agate, X. Tsampoula, P. Fischer, C. T. A. Brown, W. Sibbett, A. Riches, F. Gunn-Moore, and K. Dholakia, “Femtosecond optical transfection of cells: viability and efficiency,” Opt. Express 14(16), 7125–7133 (2006). [CrossRef] [PubMed]

]. Although the deployment of femtosecond lasers is not a prerequisite in photoporation techniques, the exposure of cells to high intensity ultrashort optical pulses has been shown to enhance localized permeability and there is the added attraction that confocal and multi-photon optical imaging can be incorporated as complementary features within the procedural setups. In simple terms, a beam from a femtosecond laser (commonly a Ti:sapphire laser) when focused on a cell membrane induces an increased permeability through a multi-photon poration process [86

86. A. Vogel, J. Noack, G. Huttman, and G. Paltauf, “Mechanisms of femtosecond laser nanosurgery of cells and tissues,” Appl. Phys. B 81(8), 1015–1047 (2005). [CrossRef]

] such that foreign DNA in a surrounding medium, for example, can diffuse into the cell before the membrane self-heals. If this foreign DNA is transcribed and translated into protein then optical transfection is said to have occurred in the cell but where another membrane-impermeable macromolecule or object is introduced then photoporation has taken place.

Within the authors’ labs, a range of further experiments have been undertaken in this field including the tailoring of the laser beam to have Bessel-like propagation characteristics. Such a development presents a significant practical refinement because the natural movement of the membrane of living cells could be better tolerated in contrast to the criticality of the focal plane associated with a Gaussian beam, and indeed, the usual tight focusing limitations of multi-photon techniques may be eased significantly [87

87. X. Tsampoula, V. Garces-Chavez, M. Comrie, D. J. Stevenson, B. Agate, C. T. A. Brown, F. Gunn-Moore, and K. Dholakia, “Femtosecond cellular transfection using a nondiffracting light beam,” Appl. Phys. Lett. 91(5), 053902 (2007). [CrossRef]

]. Also, by exploiting beam manipulations using spatial light modulators it has been possible to demonstrate much more spatially versatile poration and transfection strategies involving single cells or cell clusters that make this technique increasingly user-compatible to the biology and medical research communities [88

88. T. Cižmár, V. Kollárová, X. Tsampoula, F. Gunn-Moore, W. Sibbett, Z. Bouchal, and K. Dholakia, “Generation of multiple Bessel beams for a biophotonics workstation,” Opt. Express 16(18), 14024–14035 (2008). [CrossRef] [PubMed]

]. An interesting refinement of the technique that demonstrates the flexibility offered by ultrashort pulse lasers is to use the laser operating in a CW mode to facilitate optical tweezing of a cell into a chamber control the reagent of interest. Switching the laser to femtosecond-pulse operation then provides optical poration of the cell. The laser, operating CW can then be used to move the treated cell to another region for analysis without further interaction [89

89. C. T. A. Brown, D. J. Stevenson, X. Tsampoula, C. McDougall, A. A. Lagatsky, W. Sibbett, F. J. Gunn-Moore, and K. Dholakia, “Enhanced operation of femtosecond lasers and applications in cell transfection,” J Biophotonics 1(3), 183–199 (2008). [CrossRef] [PubMed]

].

4. Developments described in this focus issue

Harth et al. [90] demonstrate how a controllable pulse duration may be obtained by modulation of the output from a CW semiconductor source. They also show that very impressive average output powers may be obtained by combining a semiconductor seed module with a solid-state amplifier. By contrast, the work of Kienle et al. [91

91. F. Kienle, P. S. Teh, D. Lin, S.-u. Alam, J. H. V. Price, D. C. Hanna, D. J. Richardson, and D. P. Shepherd, “High-power, high repetition-rate, green-pumped, picosecond LBO optical parametric oscillator,” Opt. Express 20(7), 7008–7014 (2012).

] shows that the pulsed output from a semiconductor laser may be combined with fiber amplifier modules and an optical parametric oscillator to produce a high power source of ultrashort pulses that can be tuned near-continuously from 651 nm to 2851 nm. Zhang et al. [92

92. X. Zhang, E. Schneider, G. Taft, H. Kaptyen, M. Murnane, and S. Backus, “Multi-microjoule, MHz repetition rate Ti:sapphire ultrafast regenerative amplifier system,” Opt. Express 20(7), 7015–7021 (2012).

] present results that show that tunable repetition rate, high energy, pulses (50 kHz to 1.7 MHz) with sub-60fs durations can be obtained from extremely compact amplifier configurations.

The work reported by Metzger et al. [93

93. K. Metzger, V. F. Olle, A. Wonfor, R. V. Penty, I. H. White, M. Mazilu, C. T. A. Brown, and W. Sibbett, “Algorithm-based continuous pulse duration tuning and performance control of a modelocked laser diode,” Opt. Express 20(7), 722–7034 (2012).

], Olle et al. [94

94. V. F. Olle, P. P. Vasil’ev, A. Wonfor, R. V. Penty, and I. H. White, “Ultrashort superradiant pulse generation from a GaN/InGaN heterostructure,” Opt. Express 20(7), 7035–7039 (2012).

], and Wilcox et al. [95

95. K. G. Wilcox, A. H. Quarterman, V. Apostolopoulos, H. E. Beere, I. Farrer, D. A. Ritchie, and A. C. Tropper, “175 GHz, 400-fs-pulse harmonically mode-locked surface emitting semiconductor laser,” Opt. Express 20(7), 7040–7045 (2012).

] concentrates on semiconductor ultrashort-pulse laser technology. By combining established VECSEL technology with harmonic mode locking techniques, Wilcox and associates [95

95. K. G. Wilcox, A. H. Quarterman, V. Apostolopoulos, H. E. Beere, I. Farrer, D. A. Ritchie, and A. C. Tropper, “175 GHz, 400-fs-pulse harmonically mode-locked surface emitting semiconductor laser,” Opt. Express 20(7), 7040–7045 (2012).

] demonstrate that it is possible to obtain very high repetition frequencies (175 GHz) with reasonable average output powers while eliminating Q-switching instabilities. Olle and colleagues [94

94. V. F. Olle, P. P. Vasil’ev, A. Wonfor, R. V. Penty, and I. H. White, “Ultrashort superradiant pulse generation from a GaN/InGaN heterostructure,” Opt. Express 20(7), 7035–7039 (2012).

] used novel methods to form pulses within a semiconductor laser to show that it is possible to obtain pulses with reasonably high peak powers directly from a semiconductor laser operating in the visible part of spectrum. Metzger et al. [93

93. K. Metzger, V. F. Olle, A. Wonfor, R. V. Penty, I. H. White, M. Mazilu, C. T. A. Brown, and W. Sibbett, “Algorithm-based continuous pulse duration tuning and performance control of a modelocked laser diode,” Opt. Express 20(7), 722–7034 (2012).

] show that with a careful algorithm design it is possible to obtain continuous pulse duration tuning from 500 fs to 2.2 ps directly from a very simple two-section semiconductor laser. This also provided a platform for control algorithms that automate the setup process to offer a very flexible interface and remote control tool for ultrafast lasers.

Leindecker et al. [96

96. N. Leindecker, A. Marandi, R. L. Byer, K. L. Vodopyanov, J. Jiang, I. Hartl, M. Fermann, and P. G. Schunemann, “Octave-spanning ultrafast OPO with 2.6-6.1μm instantaneous bandwidth pumped by femtosecond Tm-fiber laser,” Opt. Express 20(7), 7046–7053 (2012).

] describe how a femtosecond fiber laser operating near 2 µm can be used in combination with a degenerate OPO based on an orientation patterned GaAs nonlinear crystal to produce extremely broadband spectra in the infrared that extend over 3.5 µm centered at 4.1 µm. Such radiation has the potential for wide scale applications in atmospheric sensing and spectroscopy. In their paper, Baer et al. [97

97. C. R. E. Baer, O. H. Heckl, C. J. Saraceno, C. Schriber, C. Kränkel, T. Südmeyer, and U. Keller, “Frontiers in passively mode-locked high-power thin disk laser oscillators,” Opt. Express 20(7), 7054–7065 (2012).

] discuss the current state of the art in, and potential for thin disk femtosecond lasers. These laser systems have the potential to deliver pulses with both extremely high average and peak power thus paving the way for new applications in, for example, materials processing. Finally, Savitski et al. [98

98. V. G. Savitski, N. K. Metzger, S. Calvez, D. Burns, W. Sibbett, and C. T. A. Brown, “Optical trapping with “on-demand” two-photon luminescence using Cr:LiSAF laser with optically addressed saturable Bragg reflector,” Opt. Express 20(7), 7066–7070 (2012).

] demonstrate a proof-of-principle experiment to show how the control of the pulse duration regime can be used to obtain different responses within in application. The use of the same laser to provide optical trapping and on-demand two-photon luminescence from a laser with an optically controlled SESAM represents another aspect of practical source refinement.

5. Concluding remarks

In this paper we have reviewed briefly some state-of-the-art developments in femtosecond optical sources that are based on solid-state, semiconductor and fiber lasers. Whilst not a comprehensive overview, this serves to show that in the 21 years since the demonstration of the first self-mode-locked (KLM) Ti:sapphire laser, the overall field involving practical ultrafast lasers has continued to develop strongly and there now exists a very diverse and versatile range of ultrafast source options.

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33.

A. Giesen, H. Hugel, A. Voss, K. Wittig, U. Brauch, and H. Opower, ““Scalable Concept for Diode-Pumped High-Power Solid-State Lasers,” Appl. Phys. B 58(5), 365–372 (1994). [CrossRef]

34.

C. R. E. Baer, C. Kränkel, C. J. Saraceno, O. H. Heckl, M. Golling, R. Peters, K. Petermann, T. Südmeyer, G. Huber, and U. Keller, “Femtosecond thin-disk laser with 141 W of average power,” Opt. Lett. 35(13), 2302–2304 (2010). [CrossRef] [PubMed]

35.

T. Eidam, S. Hanf, E. Seise, T. V. Andersen, T. Gabler, C. Wirth, T. Schreiber, J. Limpert, and A. Tünnermann, “Femtosecond fiber CPA system emitting 830 W average output power,” Opt. Lett. 35(2), 94–96 (2010). [CrossRef] [PubMed]

36.

P. Russbueldt, T. Mans, G. Rotarius, J. Weitenberg, H. D. Hoffmann, and R. Poprawe, “400W Yb:YAG Innoslab fs-Amplifier,” Opt. Express 17(15), 12230–12245 (2009). [CrossRef] [PubMed]

37.

S. Pekarek, T. Südmeyer, S. Lecomte, S. Kundermann, J. M. Dudley, and U. Keller, “Self-referenceable frequency comb from a gigahertz diode-pumped solid-state laser,” Opt. Express 19(17), 16491–16497 (2011). [CrossRef] [PubMed]

38.

A. A. Lagatsky, C. G. Leburn, C. T. A. Brown, W. Sibbett, S. A. Zolotovskaya, and E. U. Rafailov, “Ultrashort-pulse lasers passively mode locked by quantum-dot-based saturable absorbers,” Prog. Quantum Electron. 34(1), 1–45 (2010). [CrossRef]

39.

T. R. Schibli, K. Minoshima, H. Kataura, E. Itoga, N. Minami, S. Kazaoui, K. Miyashita, M. Tokumoto, and Y. Sakakibara, “Ultrashort pulse-generation by saturable absorber mirrors based on polymer-embedded carbon nanotubes,” Opt. Express 13(20), 8025–8031 (2005). [CrossRef] [PubMed]

40.

Z. P. Sun, T. Hasan, F. Torrisi, D. Popa, G. Privitera, F. Q. Wang, F. Bonaccorso, D. M. Basko, and A. C. Ferrari, “Graphene mode-locked ultrafast laser,” ACS Nano 4(2), 803–810 (2010). [CrossRef] [PubMed]

41.

K. F. Mak, M. Y. Sfeir, Y. Wu, C. H. Lui, J. A. Misewich, and T. F. Heinz, “Measurement of the optical conductivity of graphene,” Phys. Rev. Lett. 101(19), 196405 (2008). [CrossRef] [PubMed]

42.

R. W. Newson, J. Dean, B. Schmidt, and H. M. van Driel, “Ultrafast carrier kinetics in exfoliated graphene and thin graphite films,” Opt. Express 17(4), 2326–2333 (2009). [CrossRef] [PubMed]

43.

J. R. Buckley, F. W. Wise, F. O. Ilday, and T. Sosnowski, “Femtosecond fiber lasers with pulse energies above 10 nJ,” Opt. Lett. 30(14), 1888–1890 (2005). [CrossRef] [PubMed]

44.

A. Sell, G. Krauss, R. Scheu, R. Huber, and A. Leitenstorfer, “8-fs pulses from a compact Er:fiber system: quantitative modeling and experimental implementation,” Opt. Express 17(2), 1070–1077 (2009). [CrossRef] [PubMed]

45.

G. Sobon, K. Krzempek, P. Kaczmarek, K. M. Abramski, and M. Nikodem, “10 GHz passive harmonic mode-locking in Er-Yb double-clad fiber laser,” Opt. Commun. 284(18), 4203–4206 (2011). [CrossRef]

46.

S. Lefrançois, K. Kieu, Y. J. Deng, J. D. Kafka, and F. W. Wise, “Scaling of dissipative soliton fiber lasers to megawatt peak powers by use of large-area photonic crystal fiber,” Opt. Lett. 35(10), 1569–1571 (2010). [CrossRef] [PubMed]

47.

B. Oktem, C. Ülgüdür, and F. Ö. Ilday, “Soliton-similariton fibre laser,” Nat. Photonics 4(5), 307–311 (2010). [CrossRef]

48.

G. Marra, R. Slavík, H. S. Margolis, S. N. Lea, P. Petropoulos, D. J. Richardson, and P. Gill, “High-resolution microwave frequency transfer over an 86-km-long optical fiber network using a mode-locked laser,” Opt. Lett. 36(4), 511–513 (2011). [CrossRef] [PubMed]

49.

J. R. Unruh, E. S. Price, R. G. Molla, L. Stehno-Bittel, C. K. Johnson, and R. Q. Hui, “Two-photon microscopy with wavelength switchable fiber laser excitation,” Opt. Express 14(21), 9825–9831 (2006). [CrossRef] [PubMed]

50.

R. R. Thomson, N. D. Psaila, S. J. Beecher, and A. K. Kar, “Ultrafast laser inscription of a high-gain Er-doped bismuthate glass waveguide amplifier,” Opt. Express 18(12), 13212–13219 (2010). [CrossRef] [PubMed]

51.

N. Nishizawa and J. Takayanagi, “Octave spanning high-quality supercontinuum generation in all-fiber system,” J. Opt. Soc. Am. B 24(8), 1786–1792 (2007). [CrossRef]

52.

E. U. Rafailov, M. A. Cataluna, W. Sibbett, N. D. Il'inskaya, Y. M. Zadiranov, A. E. Zhukov, V. M. Ustinov, D. A. Livshits, A. R. Kovsh, and N. N. Ledentsov, “High-power picosecond and femtosecond pulse generation from a two-section mode-locked quantum-dot laser,” Appl. Phy. Lett. 87(2005).

53.

P. P. Vasil'ev, “Femtosecond superradiant emission in inorganic semiconductors,” Rep. Prog. Phys. 72(7), 076501 (2009). [CrossRef]

54.

M. Xia, R. V. Penty, I. H. White, and P. P. Vasil'ev, “Superradiant Emission from a Tapered Quantum-Dot Semiconductor Diode Emitter,” 2010 Conference on Lasers and Electro-Optics (CLEO) and Quantum Electronics and Laser Science Conference (QELS) (2010).

55.

U. Keller and A. C. Tropper, ““Passively modelocked surface-emitting semiconductor lasers,” Phys. Rep.-Rev. Sec. Phys. Lett. 429, 67–120 (2006).

56.

A. H. Quarterman, K. G. Wilcox, V. Apostolopoulos, Z. Mihoubi, S. P. Elsmere, I. Farrer, D. A. Ritchie, and A. Tropper, “A passively mode-locked external-cavity semiconductor laser emitting 60-fs pulses,” Nat. Photonics 3(12), 729–731 (2009). [CrossRef]

57.

M. Hoffmann, O. D. Sieber, V. J. Wittwer, I. L. Krestnikov, D. A. Livshits, Y. Barbarin, T. Südmeyer, and U. Keller, “Femtosecond high-power quantum dot vertical external cavity surface emitting laser,” Opt. Express 19(9), 8108–8116 (2011). [CrossRef] [PubMed]

58.

K. G. Wilcox, A. H. Quarterman, H. Beere, D. A. Ritchie, and A. C. Tropper, “High Peak Power Femtosecond Pulse Passively Mode-Locked Vertical-External-Cavity Surface-Emitting Laser,” IEEE Photon. Technol. Lett. 22(14), 1021–1023 (2010). [CrossRef]

59.

A. M. Weiner, D. E. Leaird, J. S. Patel, and J. R. Wullert, “Programmable Shaping of Femtosecond Optical Pulses by Use of 128-Element Liquid-Crystal Phase Modulator,” IEEE J. Quantum Electron. 28(4), 908–920 (1992). [CrossRef]

60.

J. Garduño-Mejía, A. H. Greenaway, and D. T. Reid, “Designer femtosecond pulses using adaptive optics,” Opt. Express 11(17), 2030–2040 (2003). [CrossRef] [PubMed]

61.

N. K. Metzger, W. Lubeigt, D. Burns, M. Griffith, L. Laycock, A. A. Lagatsky, C. T. A. Brown, and W. Sibbett, “Ultrashort-pulse laser with an intracavity phase shaping element,” Opt. Express 18(8), 8123–8134 (2010). [CrossRef] [PubMed]

62.

V. G. Savitski, A. J. Kemp, S. Calvez, and D. Burns, “Optically Pumped Saturable Bragg Reflectors: Nonlinear Spectroscopy and Application in Ultrafast Lasers,” IEEE J. Quantum Electron. 46(11), 1650–1655 (2010). [CrossRef]

63.

X. M. Liu, E. U. Rafailov, D. Livshits, and D. Turchinovich, “Quantum well saturable absorber mirror with electrical control of modulation depth,” Appl. Phys. Lett. 97(5), 051103 (2010). [CrossRef]

64.

S. A. Zolotovskaya, K. G. Wilcox, A. Abdolvand, D. A. Livshits, and E. U. Rafailov, “Electronically Controlled Pulse Duration Passively Mode-Locked Cr:Forsterite Laser,” IEEE Photon. Technol. Lett. 21(16), 1124–1126 (2009). [CrossRef]

65.

J. Chen, J. W. Sickler, P. Fendel, E. P. Ippen, F. X. Kärtner, T. Wilken, R. Holzwarth, and T. W. Hänsch, “Generation of low-timing-jitter femtosecond pulse trains with 2 GHz repetition rate via external repetition rate multiplication,” Opt. Lett. 33(9), 959–961 (2008). [CrossRef] [PubMed]

66.

A. Killi, J. Dörring, U. Morgner, M. J. Lederer, J. Frei, and D. Kopf, “High speed electro-optical cavity dumping of mode-locked laser oscillators,” Opt. Express 13(6), 1916–1922 (2005). [CrossRef] [PubMed]

67.

A. H. Zewail, “Femtochemistry. Past, present, and future,” Pure Appl. Chem. 72(12), 2219–2231 (2000). [CrossRef]

68.

T. Udem, R. Holzwarth, and T. W. Hänsch, “Optical frequency metrology,” Nature 416(6877), 233–237 (2002). [CrossRef] [PubMed]

69.

R. R. Gattass and E. Mazur, “Femtosecond laser micromachining in transparent materials,” Nat. Photonics 2(4), 219–225 (2008). [CrossRef]

70.

W. H. Knox, “Ultrafast technology in telecommunications,” IEEE J. Sel. Top. Quantum Electron. 6(6), 1273–1278 (2000). [CrossRef]

71.

T. Ditmire, J. Zweiback, V. P. Yanovsky, T. E. Cowan, G. Hays, and K. B. Wharton, “Nuclear fusion from explosions of femtosecond laser-heated deuterium clusters,” Nature 398(6727), 489–492 (1999). [CrossRef]

72.

W. Denk, J. H. Strickler, and W. W. Webb, “Two-photon laser scanning fluorescence microscopy,” Science 248(4951), 73–76 (1990). [CrossRef] [PubMed]

73.

K. König, A. Ehlers, I. Riemann, S. Schenkl, R. Bückle, and M. Kaatz, “Clinical two-photon microendoscopy,” Microsc. Res. Tech. 70(5), 398–402 (2007). [CrossRef] [PubMed]

74.

R. P. J. Barretto, T. H. Ko, J. C. Jung, T. J. Wang, G. Capps, A. C. Waters, Y. Ziv, A. Attardo, L. Recht, and M. J. Schnitzer, “Time-lapse imaging of disease progression in deep brain areas using fluorescence microendoscopy,” Nat. Med. 17(2), 223–228 (2011). [CrossRef] [PubMed]

75.

X. S. Xie and J. X. Cheng, “Coherent anti-Stokes Raman scattering microscopy: Instrumentation, theory, and applications,” J. Phys. Chem. B 108(3), 827–840 (2004). [CrossRef]

76.

X. S. Xie, C. W. Freudiger, W. Min, G. R. Holtom, B. W. Xu, and M. Dantus, “Highly specific label-free molecular imaging with spectrally tailored excitation-stimulated Raman scattering (STE-SRS) microscopy,” Nat. Photonics 5(2), 103–109 (2011). [CrossRef]

77.

T. Juhasz, H. Frieder, R. M. Kurtz, C. Horvath, J. F. Bille, and G. Mourou, “Corneal refractive surgery with femtosecond lasers,” IEEE J. Sel. Top. Quantum Electron. 5(4), 902–910 (1999). [CrossRef]

78.

N. Mamalis, “Femtosecond laser: the future of cataract surgery?” J. Cataract Refract. Surg. 37(7), 1177–1178 (2011). [CrossRef] [PubMed]

79.

P. S. Binder, “Flap dimensions created with the IntraLase FS laser,” J. Cataract Refract. Surg. 30(1), 26–32 (2004). [CrossRef] [PubMed]

80.

W. Sekundo, K. Kunert, C. Russmann, A. Gille, W. Bissmann, G. Stobrawa, M. Sticker, M. Bischoff, and M. Blum, “First efficacy and safety study of femtosecond lenticule extraction for the correction of myopia: six-month results,” J. Cataract Refract. Surg. 34(9), 1513–1520 (2008). [CrossRef] [PubMed]

81.

L. Kessel, L. Eskildsen, M. van der Poel, and M. Larsen, “Non-invasive bleaching of the human lens by femtosecond laser photolysis,” PLoS ONE 5(3), e9711 (2010). [CrossRef] [PubMed]

82.

K. Kuetemeyer, G. Kensah, M. Heidrich, H. Meyer, U. Martin, I. Gruh, and A. Heisterkamp, “Two-photon induced collagen cross-linking in bioartificial cardiac tissue,” Opt. Express 19(17), 15996–16007 (2011). [CrossRef] [PubMed]

83.

U. K. Tirlapur and K. König, “Targeted transfection by femtosecond laser,” Nature 418(6895), 290–291 (2002). [CrossRef] [PubMed]

84.

C. McDougall, D. J. Stevenson, C. T. A. Brown, F. Gunn-Moore, and K. Dholakia, “Targeted optical injection of gold nanoparticles into single mammalian cells,” J Biophotonics 2(12), 736–743 (2009). [CrossRef] [PubMed]

85.

D. Stevenson, B. Agate, X. Tsampoula, P. Fischer, C. T. A. Brown, W. Sibbett, A. Riches, F. Gunn-Moore, and K. Dholakia, “Femtosecond optical transfection of cells: viability and efficiency,” Opt. Express 14(16), 7125–7133 (2006). [CrossRef] [PubMed]

86.

A. Vogel, J. Noack, G. Huttman, and G. Paltauf, “Mechanisms of femtosecond laser nanosurgery of cells and tissues,” Appl. Phys. B 81(8), 1015–1047 (2005). [CrossRef]

87.

X. Tsampoula, V. Garces-Chavez, M. Comrie, D. J. Stevenson, B. Agate, C. T. A. Brown, F. Gunn-Moore, and K. Dholakia, “Femtosecond cellular transfection using a nondiffracting light beam,” Appl. Phys. Lett. 91(5), 053902 (2007). [CrossRef]

88.

T. Cižmár, V. Kollárová, X. Tsampoula, F. Gunn-Moore, W. Sibbett, Z. Bouchal, and K. Dholakia, “Generation of multiple Bessel beams for a biophotonics workstation,” Opt. Express 16(18), 14024–14035 (2008). [CrossRef] [PubMed]

89.

C. T. A. Brown, D. J. Stevenson, X. Tsampoula, C. McDougall, A. A. Lagatsky, W. Sibbett, F. J. Gunn-Moore, and K. Dholakia, “Enhanced operation of femtosecond lasers and applications in cell transfection,” J Biophotonics 1(3), 183–199 (2008). [CrossRef] [PubMed]

90..

F. Harth, T. Ulm, M. Lührmann, R. Knappe, A. Klehr, Th. Hoffmann, G. Erbert, and J. A. L’huillier, “High power laser pulses with voltage controlled durations of 400 – 1000 ps,” Opt. Express 20(7), 7002–7007 (2012).

91.

F. Kienle, P. S. Teh, D. Lin, S.-u. Alam, J. H. V. Price, D. C. Hanna, D. J. Richardson, and D. P. Shepherd, “High-power, high repetition-rate, green-pumped, picosecond LBO optical parametric oscillator,” Opt. Express 20(7), 7008–7014 (2012).

92.

X. Zhang, E. Schneider, G. Taft, H. Kaptyen, M. Murnane, and S. Backus, “Multi-microjoule, MHz repetition rate Ti:sapphire ultrafast regenerative amplifier system,” Opt. Express 20(7), 7015–7021 (2012).

93.

K. Metzger, V. F. Olle, A. Wonfor, R. V. Penty, I. H. White, M. Mazilu, C. T. A. Brown, and W. Sibbett, “Algorithm-based continuous pulse duration tuning and performance control of a modelocked laser diode,” Opt. Express 20(7), 722–7034 (2012).

94.

V. F. Olle, P. P. Vasil’ev, A. Wonfor, R. V. Penty, and I. H. White, “Ultrashort superradiant pulse generation from a GaN/InGaN heterostructure,” Opt. Express 20(7), 7035–7039 (2012).

95.

K. G. Wilcox, A. H. Quarterman, V. Apostolopoulos, H. E. Beere, I. Farrer, D. A. Ritchie, and A. C. Tropper, “175 GHz, 400-fs-pulse harmonically mode-locked surface emitting semiconductor laser,” Opt. Express 20(7), 7040–7045 (2012).

96.

N. Leindecker, A. Marandi, R. L. Byer, K. L. Vodopyanov, J. Jiang, I. Hartl, M. Fermann, and P. G. Schunemann, “Octave-spanning ultrafast OPO with 2.6-6.1μm instantaneous bandwidth pumped by femtosecond Tm-fiber laser,” Opt. Express 20(7), 7046–7053 (2012).

97.

C. R. E. Baer, O. H. Heckl, C. J. Saraceno, C. Schriber, C. Kränkel, T. Südmeyer, and U. Keller, “Frontiers in passively mode-locked high-power thin disk laser oscillators,” Opt. Express 20(7), 7054–7065 (2012).

98.

V. G. Savitski, N. K. Metzger, S. Calvez, D. Burns, W. Sibbett, and C. T. A. Brown, “Optical trapping with “on-demand” two-photon luminescence using Cr:LiSAF laser with optically addressed saturable Bragg reflector,” Opt. Express 20(7), 7066–7070 (2012).

99.

J. Köhler, M. Wollenhaupt, T. Bayer, C. Sarpe, and T. Baumert, “Zeptosecond precision pulse shaping,” Opt. Express 19(12), 11638–11653 (2011). [CrossRef] [PubMed]

OCIS Codes
(140.4050) Lasers and laser optics : Mode-locked lasers
(170.0170) Medical optics and biotechnology : Medical optics and biotechnology
(170.7160) Medical optics and biotechnology : Ultrafast technology
(320.7090) Ultrafast optics : Ultrafast lasers

ToC Category:
Ultrafast Optics

History
Original Manuscript: November 28, 2011
Revised Manuscript: January 26, 2012
Manuscript Accepted: January 30, 2012
Published: March 13, 2012

Virtual Issues
(2012) Advances in Optics and Photonics
Vol. 7, Iss. 5 Virtual Journal for Biomedical Optics
Modular Ultrafast Lasers (Invited Only) (2012) Optics Express

Citation
W. Sibbett, A. A. Lagatsky, and C. T. A. Brown, "The development and application of femtosecond laser systems," Opt. Express 20, 6989-7001 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-7-6989


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